JP4556025B2 - Direct wave arrival direction estimation device - Google Patents

Description

  The present invention relates to a direct wave arrival direction estimation device that estimates the arrival direction of a direct wave of a coherent wave.

  In an environment where radio waves such as indoors and underground shopping streets propagate through multipaths, a plurality of reflected waves arrive from various directions. In this case, the reflected wave and the direct wave are coherent waves having different phases.

  As a method of estimating the arrival directions of reflected waves and direct waves composed of such coherent waves, a method using the delay time of each wave is known (Patent Document 1). This method is a method of receiving a radio wave transmitted from a transmitting device installed on a target object and estimating the direction of the target object, that is, the arrival direction of a direct wave based on the received radio wave.

  The transmitting device transmits radio waves by spreading the spectrum using a PN code sequence. The radio wave transmitted from the transmission device directly propagates and reaches the direction detection device, or is reflected by an obstacle and reaches the direction detection device. Therefore, the direction detection device receives radio waves in which direct waves and reflected waves from the transmission device are mixed.

  Then, the direction detection device demodulates the received radio wave and multiplies each demodulated signal by a PN code sequence while continuously delaying the demodulated demodulated signal. Thereby, the spread signal component corresponding to the direct wave included in the demodulated signal and the spread signal component corresponding to the reflected wave are respectively despread, and a received signal in which a plurality of demodulated signals are arranged in time series is obtained.

  Since the direct wave travels straight from the transmission device to the direction detection device, the delay time is the shortest. The reflected wave is reflected by the obstacle between the transmission device and the direction detection device and reaches the direction detection device. The delay time is longer than the wave.

  Therefore, among the received signals arranged in time series, the signal component that appears first is a component that corresponds to a direct wave, and the signal component that appears next is a component that corresponds to a reflected wave.

  The direction detection device converts the magnitude of each component of the received signal arranged in time series into a voltage, and emits a sound such as a buzzer based on the converted voltage. When the direction detection device faces the direction of the target object, the signal component of the direct wave has the maximum intensity, so that the buzzer sound corresponding to the direct wave is also maximized.

  Therefore, the installation direction of the direction detection device is changed in various ways to receive radio waves from the transmission device, and the installation direction of the direction detection device that maximizes the buzzer sound is estimated as the direct wave arrival direction.

Thus, the conventional direct wave arrival direction estimation method uses the difference in delay time between the direct wave and the reflected wave.
Japanese Patent Laid-Open No. 11-83970

  However, in the arrival direction estimation method described in Patent Document 1, it is necessary to transmit a radio wave by performing spectrum spread and to despread the demodulated signal obtained by demodulating the received radio wave to obtain a received signal, which makes the calculation complicated. There is a problem of becoming.

  Accordingly, the present invention has been made to solve such a problem, and an object thereof is to provide a direct wave arrival direction estimation device capable of estimating the arrival direction of a direct wave composed of coherent waves by a simple calculation. It is.

  According to the present invention, the direct wave arrival direction estimation apparatus includes an array antenna and first to third estimation means. An array antenna is composed of a plurality of antenna elements. When the array antenna is present at the first position, the first estimation means includes L direct waves of radio waves radiated from the transmission source and L-1 (L is an integer of 2 or more) reflected waves. The L first arrival angles corresponding to the arriving waves are estimated using the spatial averaging method, and the first estimated arrival angles whose components are the estimated L first arrival angles are held. The second estimation means estimates the L second arrival angles corresponding to the L arrival waves using the spatial averaging method when the array antenna is present at a second position different from the first position. The second estimated arrival angle having the estimated L second arrival angles as components is held. The third estimating means associates the first estimated arrival angle and the second estimated arrival angle for each component, and calculates an absolute value of a difference between each associated first arrival angle and second arrival angle. The L arrival angle differences are obtained by calculation, and the first and second arrival angles when the maximum arrival angle difference among the obtained L arrival angle differences is obtained are the first and second arrival angles, respectively. The direction of arrival of the direct wave at the position is estimated.

  Preferably, the second estimating means is configured such that when all of the L arrival angle differences are smaller than the reference value, the L second values when the array antenna is present at a third position different from the second position. An arrival angle is estimated, and a second estimated arrival angle whose components are the estimated L second arrival angles is held.

  Preferably, the array antenna includes a feed element, 2L-1 parasitic elements loaded with variable capacitance elements, and a control circuit for controlling the capacitance of the variable capacitance elements loaded on the 2L-1 parasitic elements. Including.

  Preferably, the array antenna includes 2L antenna elements.

  In the direct wave arrival direction estimation apparatus according to the present invention, the arrival angles of L arrival waves are estimated at each of the two positions. Then, the angle difference between the components of the L estimated arrival angles estimated at the two positions is calculated, and the arrival angle when the maximum angle difference is obtained among the calculated L angle differences is directly Presumed to be the direction of arrival of waves. In other words, in the present invention, the arrival direction of the direct wave is estimated using the fact that the arrival angle of the direct wave arriving at each position is larger than the arrival angle of the reflected wave.

  Therefore, according to the present invention, it is not necessary to calculate spread spectrum using a PN code sequence, and the arrival direction of a direct wave composed of a coherent wave can be estimated by a simple calculation.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment 1]
FIG. 1 is a schematic diagram of an arrival direction estimation apparatus according to Embodiment 1 of the present invention. Referring to FIG. 1, arrival direction estimation apparatus 100 according to Embodiment 1 includes array antenna 10, directivity switching means 20, and direction estimation means 30.

  Array antenna 10 includes antenna elements 1 to 9 and varactor diodes 11 to 18. The antenna elements 1 to 9 are arranged on the xy plane (predetermined plane) along the z axis in the xyz orthogonal coordinates including the x axis, the y axis, and the z axis.

  FIG. 2 is a plan layout view of the antenna elements 1 to 9 in the xy plane shown in FIG. Referring to FIG. 2, antenna elements 1 to 9 are arranged in a square with antenna element 5 as the center. That is, the antenna elements 1 to 9 are arranged in two-dimensional rectangular symmetry with the antenna element 5 as the center.

  Referring to FIG. 1 again, antenna element 5 is a feeding element, and antenna elements 1 to 4 and 6 to 9 are parasitic elements. Varactor diodes 11-18 are connected between antenna elements 1-4, 6-9 and the ground node, respectively. Thereby, the varactor diodes 11 to 18 which are variable capacitance elements are loaded on the antenna elements 1 to 4 and 6 to 9 which are parasitic elements, respectively.

  As described above, the array antenna 10 includes nine antenna elements including one feeding element (antenna element 5) and eight parasitic elements (antenna elements 1 to 4, 6 to 9). It consists of a structure arranged symmetrically with a two-dimensional rectangle around the center.

  Directivity switching means 20 supplies control voltage sets CVL1 to CVL8 to varactor diodes 11 to 18, respectively, to switch the directivity of array antenna 10. The capacity (reactance value) of the varactor diodes 11 to 18 varies depending on the control voltages CVL1 to CVL8. The directivity switching means 20 determines the voltage values of the control voltages CVL1 to CVL8 so that the reactance value in each of the varactor diodes 11 to 18 becomes “hi” (maximum value) or “lo” (minimum value). Voltage sets CVL1-CVL8 are supplied to varactor diodes 11-18.

In this case, directivity switching means 20, the reactance value _x m1 _{~x m8} set _{x m} varactor control voltage set CVL1~CVL8 to vary as shown in Table 1 diode in the varactor diode 11 to 18 11 to 18 To supply.

When all of the reactance values x _{m1 to} x _m8 are “hi” (m = 0), the array antenna 10 has a beam pattern BPM0 including a pattern close to an omni pattern having sensitivity in all directions. Further, when the reactance value x _m1 is “lo” and the reactance values x _{m2 to} x _m8 are “hi” (m = 1), the array antenna 10 has a direction of 0 degrees (in the x-axis direction shown in FIG. 1). It has a beam pattern BPM1 having directivity in the direction of 0 degree in the positive direction.

Furthermore, when the reactance value x _m2 is “lo” and the reactance values x _m1 , x _{m3 to} x _m8 are “hi” (m = 2), the array antenna 10 has directivity in the direction of 45 degrees. It has a beam pattern BPM2.

Similarly, when the reactance values x _{m3 to} x _m8 are “lo” and the other reactance values are “hi” (m = 3 to 8), the array antenna 10 is 90 degrees, 135 Beam patterns BPM3 to BPM8 having directivity in directions of degrees, 180 degrees, 225 degrees, 270 degrees, and 315 degrees (see FIG. 2).

Thus, the directivity switching means 20 changes the reactance values x _{m1 to} x _m8 of the varactor diodes 11 to 18 loaded on the antenna elements 1 to 4 and 6 to 9 which are parasitic elements, thereby changing the array antenna 10. Switch directivity.

The direction estimation means 30 is connected to the antenna element 5 which is a feeding element of the array antenna 10, and the received signal y _m (t) when the beam pattern of the array antenna 10 is switched to the beam patterns BPM1 to BPM8 shown in FIG. Is received from the antenna element 5. Then, the direction estimating means 30 estimates the arrival direction of the direct wave composed of coherent waves arriving at the array antenna 10 based on the received signal y _m (t) by a method described later.

  In the present invention, a coherent wave having an azimuth indicating a direction in the xy plane shown in FIG. FIG. 3 is a diagram illustrating the definition of the azimuth angle.

  With reference to FIG. 3, the azimuth angle φ is defined as an angle in which the positive direction of the x axis is 0 degree in the xy plane.

Consider an environment in which L (L is a positive integer) coherent waves arrive at the array antenna 10. When each of the L coherent waves arrives from the direction (φ _k ) (k = 1, 2,..., L) with a complex amplitude s _k (t), the reactance value set x _m (= x _m1 to The received signal vector <Y (t)> obtained by x _m8 ) is expressed by the following equation.

However, <W> is an equivalent weight matrix, <a (φ _k)> is a mode vector indicating the direction of arrival of the incident wave, n (t) is the thermal noise, T is the transpose Represent. Further, thermal noise n (t) is the average is zero, the variance is sigma ^2.

In this specification, the notation <A> means a matrix A or a vector A. Therefore, notation <W> represents a matrix W in the formula (1), denoted <a (phi _k)> represents the vector a (phi _k) in equation (1).

When the directivity of the array antenna 10 is sequentially switched by the directivity switching means 20, the direction estimation means 30 receives the received signal vector <Y (t)> shown in Expression (1) from the antenna element 5 of the array antenna 10. To do. Then, the direction estimation unit 30 calculates a correlation matrix <R _xx > indicating a correlation between L coherent waves based on the received signal vector <Y (t)> by a method described later.

In the present invention, the correlation matrix <R _xx > is calculated using a spatial averaging method. FIG. 4 is a conceptual diagram of a subarray in array antenna 10 shown in FIG. Referring to FIG. 4, array antenna 10 including antenna elements 1 to 9 is divided into four subarrays SA1 to SA4 that can be translated. The sub-array SA1 includes antenna elements 1, 2, 4, and 5 arranged in a square, the sub-array SA2 includes antenna elements 2, 3, 5, and 6 that are arranged in a square, and the sub-array SA3 includes antenna elements that are arranged in a square. The sub-array SA4 includes antenna elements 4, 5, 7, and 8 arranged in a square shape. Therefore, each of the four subarrays SA1 to SA4 includes four antenna elements including the feeding element 5, and the subarrays SA1 to SA4 are movable in parallel with each other.

  Thus, in the present invention, each subarray includes the feed element 5 and the antenna elements 1 to 9 are divided into four subarrays SA1 to SA4 so that they can move in parallel.

When the antenna elements 1 to 9 are divided into four subarrays SA1 to SA4, a correlation matrix <R _xx > is calculated based on the four subarrays SA1 to SA4 by applying a spatial averaging method. In this case, there are two methods for applying the spatial averaging method. The first method is the forward spatial averaging method, and the second method is the forward / reverse spatial averaging method. Hereinafter, a method of calculating the correlation matrix <R _xx > by applying these two spatial averaging methods and estimating the arrival direction based on the calculated correlation matrix <R _xx > will be described.

[When forward spatial averaging is applied]
Forward spatial smoothing obtains four partial correlation matrix for the four subarrays SA1 to SA4 calculates the partial correlation matrix of each sub-array _{SA1~SA4 <R xx_sub1> ~ <R} xx_sub4>, 4 -part with the determined a correlation matrix _{<R xx_sub1> ~} correlation matrix by averaging the _{<R xx_sub4>} method for obtaining the _{<R xx>.}

Assuming that the received signal vector of the subarray SA1 is <Y ₁ (t)>, the subarray SA1 is composed of antenna elements 1, 2, 4, and 5. Therefore, the received signal vector <Y ₁ (t)> is expressed by the following equation. It is.

Similarly, reception signal vectors <Y ₂ (t)> to <Y ₄ (t)> of subarrays SA2 to SA4 are represented by the following equations (3) to (5), respectively.

Then, the partial correlation matrix < _{Rxx_sub1} > of the subarray SA1 is represented by the following equation.

  H represents Hermitian transpose. Further, E [•] is a time average assuming an ergoat property.

Similarly, the partial correlation matrices <R _{xx_sub2} > to <R _{xx_sub4} > of the subarrays SA2 to SA4 are represented by the following expressions (7) to (9), respectively.

Then, an average of the four partial correlation matrices <R _{xx_sub1} > to <R _{xx_sub4} > is calculated to obtain a correlation matrix <R _xx > by the following equation.

  In this way, by applying the spatial averaging method, an incoming wave degenerated into one coherent wave can be decomposed into L coherent waves.

The partial correlation matrices <R _{xx_sub1} > to <R _{xx_sub4} > expressed by the equations (6) to (9) are obtained when the subarray SA1 is translated in the order of the subarray SA2, the subarray SA3, and the subarray SA4, ie, the subarray SA1. It is a partial correlation matrix when translated in one direction (clockwise). Therefore, calculating the average of the four partial correlation matrices <R _{xx_sub1} > to <R _{xx_sub4} > when the subarray SA1 is translated in one direction is referred to as a forward spatial averaging method.

Therefore, the correlation matrix <R _xx > calculated by Expression (10) is a correlation matrix obtained by applying the forward spatial averaging method.

Note that the forward spatial averaging method not only averages the partial correlation matrices <R _{xx_sub1} > to <R _{xx_sub4} > when the subarray 1 is translated clockwise, but also translates the subarray 1 counterclockwise. This includes the case where the four partial correlation matrices are averaged. That is, the forward spatial averaging method may calculate four partial correlation matrices when the subarray SA1 is translated in the order of the subarray SA4, the subarray SA3, and the subarray SA2, and may average the four calculated partial correlation matrices. Including.

When the correlation matrix _{<R xx>} is computed, the correlation matrix is subjected to eigenvalue decomposition to _{<R xx> MUSIC (MUltiple SIgnal} Classification) spectrum _{P MUSIC} a (phi) is calculated by the following equation.

However, the mode vector <a _sub (φ)> is [a ₁ (φ),..., A ₄ (φ)] ^T , and <E _N > is an eigenvalue decomposition of the correlation matrix <R _xx >. Is the eigenvector [e _{L + 1} ,..., E ₄ ] of the noise at the time.

[For forward / reverse spatial averaging method]
The forward / reverse spatial averaging method is a forward part composed of an average of four partial correlation matrices <R _{xx_sub_f1} > to <R _{xx_sub_f4} > when the subarray SA1 is translated in the order of the subarray SA2, the subarray SA3, and the subarray SA4. correlation matrix and _{<R xx_f>,} subarrays SA1 subarrays SA4, 4-part correlation matrix when moving parallel in the order of sub-arrays SA3 and subarray _{SA2 <R xx_sub_b1> ~} backward partial correlation matrix of the average _{<R xx_sub_b4>} It calculates a _<R xx_b>, is a method for obtaining the calculated forward partial correlation matrix _{<R xx_f>} and backward partial correlation matrix averaging operation on the correlation matrix of the _{<R xx_b><Rxx>} .

Since the four partial correlation matrices <R _{xx_sub_f1} > to <R _{xx_sub_f4} > are expressed by the above-described equations (6) to (9), the forward partial correlation matrix <R _{xx_f} > is expressed by the above-described equation (10). Represented.

Next, how to obtain the reverse partial correlation matrix <R _{xx — b} > will be described.

Assuming that the backward input vector to the entire antenna elements 1 to 9 is <Y _b (t)>, the backward input vector <Y _b (t)> is expressed by the following equation.

  However, * represents a complex conjugate. The matrix <J> is an m-order square matrix represented by the following equation.

The backward input vector <Y _b (t)> in equation (12) is similar to the same type and the same shape as the received signal vector <Y (t)> in equation (1) except that the phase relationship of each incoming signal is different. Can be considered. Using this phase relationship for phase averaging of the spatial average, the correlation matrix by the backward input vector <Y _b (t)> is also incorporated into the spatial average element.

The backward input vector <Y _b (t)> shown in Expression (12) is divided into subarrays SA1 to SA4, and four partial correlation matrices <R are obtained by the same method as Expressions (6) to (9) described above. _{xx_b_sub1} > to < _{Rxx_b_sub4} > are calculated, and the calculated four partial correlation matrices < _{Rxx_b_sub1} > to < _{Rxx_b_sub4} > are averaged to calculate a reverse partial correlation matrix < _{Rxx_b} >.

If the reverse input vector of the sub-array SA1 is <Y _b1 (t)>, the sub-array SA1 is composed of the antenna elements 1, 2, 4, and 5. Therefore, the reverse input vector <Y _b1 (t)> is It is expressed by the formula.

Similarly, the backward input vectors <Y _b2 (t)> to <Y _b4 (t)> of the subarrays SA2 to SA4 are represented by the following equations (15) to (17), respectively.

Then, the partial correlation matrix < _{Rxx_b_sub1} > of the subarray SA1 is represented by the following equation.

Partial correlation matrix of the subarray SA2~SA4 similarly _{<R xx_b_sub2> ~ <R xx_b_sub4} > are each represented by the following equation (19) to (21).

Then, the average of the four partial correlation matrices <R _{xx_b_sub1} > to <R _{xx_b_sub4} > is calculated to obtain the backward partial correlation matrix <R _{xx_b} > by the following equation.

Since the forward partial correlation matrix <R _xx — _f > = <R _xx >, the correlation matrix <R _xx ^fb > when the forward / reverse spatial averaging method is applied is expressed by the following equation.

  In this way, by applying the spatial averaging method, an incoming wave degenerated into one coherent wave can be decomposed into L coherent waves.

The arrival direction when the forward / reverse spatial averaging method is applied can be estimated by performing eigenvalue decomposition on the correlation matrix <R _xx ^fb > obtained by the above-described method and calculating the MUSIC spectrum.

  By applying the forward / reverse spatial averaging method, subarray SA1 is translated in the order of subarray SA2, subarray SA3, and subarray SA4, and further, subarray SA1 is translated in the order of subarray SA4, subarray SA3, and subarray SA2. The number of subarrays for calculating the partial correlation matrix can be substantially increased, and the number of directions of arrival that can be estimated can be increased.

  In the above description, the case where the antenna elements 1 to 9 of the array antenna 10 are divided into four subarrays SA1 to SA4 each consisting of four antenna elements and the spatial averaging method is applied has been described. The antenna elements 1 to 9 may be divided into subarrays.

  FIG. 5 is a diagram for explaining the principle of estimating the arrival direction of a direct wave. When the array antenna 10 is installed at the measurement point 1, it receives the direct wave WV1 from the transmission source S and the reflected wave WV2. Since the reflected wave WV2 corresponds to a direct wave from the mirror image point S ′ of the transmission source S, the array antenna 10 is illustrated in FIG. 5 so as to directly receive the reflected wave WV2 from the mirror image point S ′. .

In this case, the array antenna 10 receives the direct wave WV1 from a direction that forms an angle θ ₁ with respect to the normal direction of the array antenna 10 (the y-axis direction shown in FIG. 1), and the normal direction of the array antenna 10 receiving a reflected wave WV2 from a direction forming an angle theta _2.

On the other hand, when the array antenna 10 is installed at the measurement point 2, the array antenna 10 receives the direct wave WV1 ′ from a direction that forms an angle θ ₁ ′ with respect to the normal direction of the array antenna 10, and the normal direction of the array antenna 10. The reflected wave WV2 ′ is received from the direction that forms the angle θ ₂ ′.

The angle difference Δθ ₁ = abs (θ ₁ −θ ₁ ′) between the angle θ ₁ and the angle θ ₁ ′ is equal to the angle difference Δθ ₂ = abs (θ ₂ −θ ₂ ) between the angle θ ₂ and the angle θ ₂ ′. Will always be larger than '). This is because the mirror image point S ′, which is the transmission source of the reflected waves WV2, WV2 ′, is always located farther from the transmission source S of the direct waves WV1, WV1 ′, and θ ₁ > θ ₂ and θ ₁ ′> This is because θ ₂ ′ is satisfied. Note that abs (θ ₁ −θ ₁ ′) means the absolute value of (θ ₁ −θ ₁ ′).

Then, the arrival angle theta ₁ to the array antenna 10 estimated in the measuring point _1, and theta _2, the arrival angle theta ₁ to the array antenna 10 estimated in the measurement point _{2 ',} θ 2' corresponding angle between theta ₁ , Θ ₁ ′; θ ₂ , θ ₂ ′, and Δθ ₁ (= abs (θ ₁ −θ ₁ ′)), Δθ ₂ (= abs (θ ₂ −θ ₂ ′)) Of the angle differences Δθ ₁ and Δθ ₂ , the angles θ ₁ and θ ₁ ′ when the maximum angle difference is obtained are the arrival angles (= arrival directions) of the direct waves WV1 and WV1 ′, respectively.

Then, the arrival angles θ ₁ , θ ₂ ; θ ₁ ′, θ ₂ ′ at the measurement points ₁ and ₂ are estimated by the MUSIC method using the spatial averaging method described above.

Accordingly, in the present invention, the direction estimating means 30 estimates the arrival angles θ ₁ and θ ₂ at the measurement point 1 by the MUSIC method using the spatial averaging method described above, and the estimated arrival angles (θ ₁ , θ _2). ) Is memorized.

Thereafter, the array antenna 10 is moved from the measurement point 1 to the measurement point 2. Then, the direction estimating means 30 estimates the arrival angles θ ₁ ′, θ ₂ ′ at the measurement point 2 by the MUSIC method using the above-described spatial averaging method, and the estimated arrival angles (θ ₁ ′, θ ₂ ′). Remember.

Subsequently, the direction estimation means 30 calculates the angle difference Δθ ₁ (= abs (θ ₁ −θ ₁ ′)), Δθ ₂ (= abs (θ ₂ −θ ₂ ′)), and the calculated angle difference Δθ. ₁ and Δθ ₂ , the angles θ ₁ and θ ₁ ′ when the maximum angle difference is obtained are estimated as the arrival angles (= arrival directions) of the direct waves WV1 and WV1 ′, respectively.

In FIG. 5, the case where the direct wave and one reflected wave arrive at the array antenna 10 has been described. However, the L waves composed of the direct wave and L−1 (L is a positive integer) reflected waves are described. When the coherent wave arrives at the array antenna 10, the arrival directions θ ₁ and θ ₁ ′ at the measurement points 1 and 2 of the direct wave can be estimated in the same manner.

FIG. 6 is a flowchart for explaining the operation of estimating the arrival direction of the direct wave. When a series of operations is started, the array antenna 10 is installed at the measurement point 1, and the arrival direction estimation apparatus 100 performs arrival direction estimation for the coherent wave using the MUSIC method based on the spatial averaging method described above, and each arrival The wave direction is estimated as {θ ₁ , θ ₂ ,..., Θ _L } (step S1).

Thereafter, the array antenna 10 is moved to the measurement point 2. Similarly, the arrival direction estimation device 100 estimates the arrival direction for the coherent wave at the measurement point 2 as {θ ₁ ′, θ ₂ ′,..., Θ _L ′} (step S2).

Subsequently, the arrival direction estimation apparatus 100 determines the angle difference between the arrival directions estimated at the measurement point 1 and the measurement point 2 {Δθ ₁ = abs (θ ₁ −θ ₁ ′), Δθ ₂ = abs (θ ₂ −θ ₂ ′). ,..., Δθ _L } are respectively calculated (step S3).

Then, the arrival direction estimation apparatus 100 determines whether or not the calculated angle differences {Δθ ₁ , Δθ ₂ ,..., Δθ _L } are larger than the resolution (step S4). When each angle difference is not larger than the resolution, the array antenna 10 is changed to a place different from the measurement point 2 (step S5), and the above-described steps S2 to S4 are repeatedly executed.

On the other hand, when it is determined in step S4 that each angle difference is larger than the resolution, the arrival direction estimating apparatus 100 determines the maximum from the angle differences {Δθ ₁ , Δθ ₂ ,..., Δθ _L } calculated in step S3. And the angles θ _j and θ _j ′ (where j is any one of 1 to L) when the extracted maximum angle difference Δθ _max is obtained are the direct waves at the measurement points 1 and 2, respectively. The direction of arrival is estimated (step S6). Thus, a series of operations is completed.

FIG. 7 is a flowchart for explaining the detailed operation of step S1 shown in FIG. When a series of operations is started, the directivity switching unit 20 supplies the control voltage sets CVL1 to CVL8 to the varactor diodes 11 to 18. The array antenna 10 receives the coherent wave by sequentially switching the directivity to the 0 degree direction, 45 degree direction, 90 degree direction, 135 degree direction, 180 degree direction, 225 degree direction, 270 degree direction, and 315 degree direction. (Step S11), the received received signals y ₁ (t), y ₂ (t),... Are output from the antenna element 5 to the direction estimating means 30.

The direction estimation means 30 substitutes the received signals y ₁ (t), y ₂ (t),..., Y _m (t) received from the array antenna 10 into the equation (1) to obtain a received signal vector <Y ( t)> is generated (step S12).

  Then, the direction estimating means 30 divides the antenna elements 1 to 9 of the array antenna 10 into a plurality of subarrays SA1 to SA4 that can be translated, and calculates a plurality of partial correlation matrices in the divided subarrays SA1 to SA4. (Step S13).

  Thereafter, the direction estimating means 30 calculates a correlation matrix by applying a spatial averaging method to the plurality of partial correlation matrices (step S14). In this case, the direction estimation unit 30 calculates the correlation matrix by applying one of the above-described forward spatial averaging method and forward / reverse spatial averaging method.

  When calculating the correlation matrix, the direction estimation unit 30 calculates the MUSIC spectrum by performing eigenvalue decomposition on the calculated correlation matrix, and estimates the arrival direction of the coherent wave based on the MUSIC spectrum (step S15). And a series of operation | movement is complete | finished.

As described above, the direction-of-arrival estimation method according to the present invention is such that L arrivals of the direct wave and n reflected waves to the array antenna 10 are performed at each of the two measurement points by the MUSIC method using the spatial averaging method. The angles {θ ₁ , θ ₂ ,..., Θ _L }, {θ ₁ ′, θ ₂ ′,..., Θ _L ′} are estimated and L arrival angles {θ ₁ at two measurement points are estimated. , Θ ₂ ,..., Θ _L }, {θ ₁ ′, θ ₂ ′,..., Θ _L ′}, the angle difference {Δθ ₁ = abs (θ ₁ −θ ₁ ′) , Δθ ₂ = abs (θ ₂ −θ ₂ ′),..., Δθ _L }, and calculate the angles θ _j and θ _j ′ when the maximum angle difference is obtained among the calculated angle differences. Estimate the arrival angle of the direct wave.

  Therefore, the arrival direction of the direct wave can be estimated without performing a complicated calculation by the spread spectrum method as in the conventional estimation method.

Note that the direction estimation means 30 for estimating the arrival angles θ ₁ , θ ₂ ,..., Θ _L of the incoming waves at the measurement point 1 according to step S1 in FIG. 6 (= steps S11 to S15 in FIG. 1st estimation means "is configured.

Further, the direction estimating means 30 for estimating the arrival angles θ ₁ ′, θ ₂ ′,..., Θ _L ′ of the incoming waves at the measurement point 2 according to step S2 in FIG. 6 (= steps S11 to S15 in FIG. 7) Constitutes "second estimation means".

  Furthermore, the direction estimating means 30 for estimating the direction of arrival of the direct wave according to steps S3, S4 and S6 in FIG. 6 constitutes a “third estimating means”.

  Furthermore, the directivity switching means 20 constitutes a “control circuit” that controls the capacitances of the variable capacitance elements 11 to 18 loaded in the parasitic elements 1 to 4 and 6 to 9.

Furthermore,
[Embodiment 2]
FIG. 8 is a schematic diagram of an arrival direction estimation apparatus according to the second embodiment. Arrival direction estimation apparatus 200 according to Embodiment 2 includes array antenna 210 and direction estimation means 220.

  Array antenna 210 includes antenna elements # 1 to #M (M is a positive integer). The antenna elements # 1 to #M are arranged linearly at equal intervals d.

  The direction estimation unit 220 estimates the arrival direction of the direct wave based on the input vector <X (t)> of the array antenna 210 by a method described later.

  FIG. 9 is a conceptual diagram of a subarray in array antenna 210 shown in FIG. Each of the subarrays SBA-1 to SBA-N (N = M−K + 1, where K is a positive integer) includes K antenna elements. More specifically, the subarray SBA-1 includes antenna elements # 1 to #K, and the subarray SBA-2 includes antenna elements # 2 to # K + 1. Similarly, the subarray SBA-N includes It consists of antenna elements # M-K + 1 to #M.

  Assuming an environment in which L coherent waves arrive at array antenna 210, the complex amplitude <F (t)> of L coherent waves arriving at array antenna 210 is expressed by the following equation.

In Expression (24), α _i (i is a positive integer) is a complex constant representing attenuation and phase delay of the i-th wave with respect to the first wave.

An input vector <X ₁ (t)> of the subarray SBA-1 is expressed by the following equation.

However, the vector <N ₁ (t)> is an internal noise vector of the subarray SBA-1. In this case, the input vector <X _n (t)> of the n-th (n = 1, 2,..., N) -th subarray SBA-n is expressed by the following equation.

  The matrix <B> in Expression (26) is an L-shaped diagonal matrix expressed by the following expression.

Further, the vector <N _n (t)> in Expression (26) is an internal noise vector of the nth sub-array SBA-n.

Accordingly, the correlation matrix R _xx ⁿ of the nth sub-array SBA-n is expressed by the following equation.

When the uniform spatial averaging method is adopted as the spatial average, the average correlation matrix <R _{xx_av} > is expressed by the following equation.

  In this way, by applying the spatial averaging method, an incoming wave degenerated into one coherent wave can be decomposed into L coherent waves.

When the average correlation matrix <R _{xx_av} > is calculated, eigenvectors [e ₁ , e ₂ ,..., E _K ] are obtained from the average correlation matrix <R _{xx_av} >, and the obtained eigenvectors [e ₁ , e ₂ , .., E _K ], using the orthonormal prescribed vector [e _{L + 1} , e _{L + 2} ,..., E _K ] in the noise subspace, the MUSIC spectrum P _MU (θ) is expressed by the following equation. The

The angles θ ₁ , θ ₂ ,..., Θ _{L at} which L peaks appear in the MUSIC spectrum P _MU (θ) are the arrival angles (= arrival directions) of the L arrival waves.

In the second embodiment, the direction estimation means 220 calculates the MUSIC spectrum P _MU (θ) by the method described above in a state where the array antenna 210 is installed at the measurement point 1 shown in FIG. The arrival angles θ ₁ and θ ₂ of the direct wave WV1 and the reflected wave WV2 are estimated based on the spectrum P _MU (θ).

The direction estimation unit 220, a state in which the array antenna 210 is installed in the measurement point 2, MUSIC spectrum _{P MU (θ)} by the method described above in the 'computes its computed MUSIC spectrum _{P MU} (theta)' Based on this, the arrival angles θ ₁ ′ and θ ₂ ′ of the direct wave WV1 ′ and the reflected wave WV2 ′ are estimated.

Thereafter, the direction estimation unit 220 estimates the arrival directions θ ₁ and θ ₁ ′ of the direct waves WV1 and WV1 ′ at the measurement points 1 and 2 by the same method as that in the first embodiment.

In this case, the direction estimation means 220 estimates the arrival angles θ ₁ and θ ₁ ′ of the direct waves WV1 and WV1 ′ according to the flowchart shown in FIG.

As described above, in the first embodiment, the directivity is directly changed using the array antenna 10 whose directivity can be switched by changing the capacitance of the varactor diodes 11 to 18 loaded in the parasitic elements 1 to 4 and 6 to 9. The estimation of the arrival angles θ ₁ and θ ₁ ′ of the waves WV1 and WV1 ′ will be described. In the second embodiment, the array antenna 210 composed of M antenna elements # 1 to #M arranged linearly. The estimation of the arrival angles θ ₁ and θ ₁ ′ of the direct waves WV1 and WV1 ′ using the above is described.

In the estimation of the arrival angles θ ₁ and θ ₁ ′ of the direct waves WV1 and WV1 ′, a case where the direct waves WV1 and WV1 ′ and one reflected wave WV2 and WV2 ′ arrive at the array antennas 10 and 210 will be described. In reality, however, there are reflected waves due to two-time reflection, reflected waves due to three-time reflection, and the like. Generally, the direct waves WV1 and WV1 ′ and the L−1 reflected waves are completely separated from each other. An incoming wave composed of L correlated coherent waves arrives at array antennas 10 and 210.

Therefore, it is necessary to determine the number of antenna elements of the array antennas 10 and 210 so that the arrival angles θ ₁ , θ ₂ ,..., Θ _L of the _L coherent waves can be estimated.

In order to accurately estimate the arrival angles θ ₁ , θ ₂ ,..., Θ _L when the number of antenna elements of the array antennas 10 and 210 is M and the number of antenna elements of the subarray is K, N = M−K + 1 ≧ L needs to be satisfied. That is, it is necessary that the number N of subarrays is equal to or greater than the number L of coherent waves. This is because the arrival angles θ ₁ , θ ₂ ,..., Θ _L of the _L coherent waves cannot be estimated unless there is a subarray that can receive L coherent waves separately and independently.

  Further, when applying the MUSIC method, it is necessary to satisfy K ≧ L + 1. Therefore, in order to hold these two inequalities, it is necessary to hold M = N + K−1 ≧ L + K−1 ≧ 2L.

  As a result, the number of antenna elements M needs to be twice as many as the expected number of incoming waves L.

  Then, the array antenna 10 shown in FIG. 1 is generally composed of one feeding element and 2L-1 parasitic elements loaded with varactor diodes. The array antenna 220 shown in FIG. Generally, it consists of 2L antenna elements.

  In the first embodiment, the array antenna 10 has been described as having a configuration in which the parasitic elements 1 to 4 and 6 to 9 are arranged in a two-dimensional rectangular shape around the feeder element 5, but in the present invention, Not limited to this, the array antenna 10 may have a configuration in which parasitic elements are arranged in a circle around the feeding elements.

In the first and second embodiments, the MUSIC method using spatial smoothing, incoming wave WV1 at each measurement point 1,2, WV2; WV1 ', WV2' arrival angle theta ₁ of, θ _2; θ ₁ ', theta _2' has been described as to estimate, the present invention is not limited thereto, the ESPRIT using spatial smoothing (estimation of Signal Parameters via Rotational Invariance techniques) method, the arrival at each measurement point 1,2 The arrival angles θ ₁ , θ ₂ ; θ ₁ ′, θ ₂ ′ of the waves WV1, WV2; WV1 ′, WV2 ′ may be estimated, and the arrival angles of the L coherent waves can be accurately estimated. Any method may be used as long as it is a method.

That is, the present invention is incoming wave WV1~WVL at two measurement points 1 and 2; 'arrival angle theta ₁ of ~θ _L; θ _1' WV1'~WVL a through? _L 'estimated by some method, the estimation arrival angle theta ₁ through? _L and; θ ₁ '~θ _L' based on the angle difference _{Δθ 1 = abs (θ 1 -θ} 1 ') ~Δθ L = abs (θ L -θ L') is calculated and The maximum angle difference Δθ _i = abs (θ _i −θ _i ′) was obtained among the angle differences Δθ ₁ = abs (θ ₁ −θ ₁ ′) to Δθ _L = abs (θ _L −θ _L ′). The arrival angles θ _i and θ _i ′ at that time may be estimated as the direct wave arrival directions at the measurement points 1 and 2, respectively.

Note that the direction estimation means 220 for estimating the arrival angles θ ₁ , θ ₂ ,..., Θ _L of the incoming waves at the measurement point 1 in accordance with step S1 in FIG. 6 constitutes a “first estimation means”.

Further, the direction estimation means 220 for estimating the arrival angles θ ₁ ′, θ ₂ ′,..., Θ _L ′ of the incoming waves at the measurement point 2 in accordance with step S2 in FIG. 6 constitutes “second estimation means”. To do.

  Furthermore, the direction estimation means 220 for estimating the arrival direction of the direct wave in accordance with steps S3, S4 and S6 in FIG. 6 constitutes a “third estimation means”.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  The present invention is applied to a direct wave arrival direction estimation device capable of estimating the arrival direction of a direct wave composed of coherent waves by a simple calculation.

It is the schematic of the arrival direction estimation apparatus by Embodiment 1 of this invention. FIG. 2 is a plan layout view of antenna elements in an xy plane shown in FIG. 1. It is a figure which shows the definition of an azimuth. It is a conceptual diagram of the subarray in the array antenna shown in FIG. It is a figure for demonstrating the principle which estimates the arrival direction of a direct wave. It is a flowchart for demonstrating the operation | movement which estimates the arrival direction of a direct wave. It is a flowchart for demonstrating the detailed operation | movement of step S1 shown in FIG. 6 is a schematic diagram of an arrival direction estimation apparatus according to Embodiment 2. FIG. It is a conceptual diagram of the subarray in the array antenna shown in FIG.

Explanation of symbols

  1 to 9, # 1 to #M antenna element, 10,210 array antenna, 11 to 18 varactor diode, 20 directivity switching means, 30,220 direction estimation means, 100,200 arrival direction estimation device, BPM0 to BPM8 beam pattern SA1-SA6, SBA-1 to SBA-N subarrays.

Claims (4)

An array antenna composed of a plurality of antenna elements;
When the array antenna is present at the first position, it corresponds to L incoming waves including a direct wave of a radio wave radiated from a transmission source and L-1 (L is an integer of 2 or more) reflected waves. First estimating means for estimating L first angles of arrival using a spatial averaging method, and holding first estimated angles of arrival having the estimated L first angles of arrival as components;
When the array antenna is present at a second position different from the first position, L second arrival angles corresponding to the L arrival waves are estimated using a spatial averaging method, and the estimation is performed. Second estimation means for holding a second estimated arrival angle having L second arrival angles as components,
The first estimated arrival angle and the second estimated arrival angle are associated for each component, and the absolute value of the difference between each associated first arrival angle and second arrival angle is calculated to be L And the first and second arrival angles when the maximum arrival angle difference among the L arrival angle differences obtained is obtained at the first and second positions, respectively. A direct wave arrival direction estimation device comprising third wave estimation means for estimating the arrival direction of the direct wave.   The second estimator is configured such that when all of the L arrival angle differences are smaller than a reference value, the L number of the second antennas when the array antenna exists at a third position different from the second position. The direct wave arrival direction estimation device according to claim 1, wherein two arrival angles are estimated and a second estimated arrival angle having the estimated L second arrival angles as components is held. The array antenna is
A feeding element;
2L-1 parasitic elements loaded with variable capacitance elements;
The direct wave arrival direction estimation apparatus according to claim 1, further comprising: a control circuit that controls a capacitance of the variable capacitance element loaded on the 2L−1 parasitic elements.   The direct wave arrival direction estimation apparatus according to claim 1 or 2, wherein the array antenna includes 2L antenna elements.

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